Accessing ZIP Files

A ZIP file (.ZIP) is a compressed archive file format. A ZIP file usually contains a single or multiple file/directory entries that have been compressed. ZIP files are often used for email attachments and backup archival purposes.

PxPlus ZIP File Support

Using PxPlus, you can:

Create and/or open a ZIP file using the OPEN [CREATE] directive.
Get metadata about all of the files/directories contained within the ZIP archive using the FIN( ) system function.
Extract and read the compressed data of the files within the ZIP archive using the READ RECORD or EXTRACT FILE directive.
Compress and append files/directories to the ZIP archive using the WRITE RECORD or INSERT FILE directive.
Remove files/directories from the ZIP archive using the REMOVE directive.

PxPlus uses a record/index to represent a file/directory entry within a ZIP file. The order of the records depends on the order that the file/directory entries were added to the ZIP archive.

PxPlus uses the key to represent the file/directory name of an entry in the ZIP file.

(PxPlus ZIP file support was added in PxPlus 2014.)

Creating a ZIP File

To create a ZIP file, use the OPEN CREATE directive with OPT="ZIP":

OPEN CREATE (chan, OPT="ZIP") "myZIPFile.zip"

Opening a ZIP File

To open a ZIP file, use the standard OPEN directive:

OPEN (chan) "myZIPFile.zip"

Getting ZIP Metadata

Use the FIN( ) system function to get metadata about the compressed files/directories within the ZIP archive. The file/directory entry that you get metadata about is the next record. If there is no next record, a null value is returned.

The "ZIPFilename" keyword returns the file/directory name of the next ZIP archive entry. Directory names will always end in a '/' (forward slash).

FIN (chan, "ZIPFilename")

The "ZIPInfo" keyword will return all of the metadata about a file/directory in a ZIP archive.

FIN (chan, "ZIPInfo")

The key system functions KEF( ), KEP( ), KEC( ), KEY( ), KEN( ) and KEL( ) can also be used to return the file/directory name of ZIP archive entries. KEY(chan) and FIN(chan, "ZIPFilename") are equivalent and will return the same file/directory name.

Extracting from a ZIP File

You can extract a file in two ways:

You can use the EXTRACT FILE directive, which will decompress the file in the archive and put it on your system. OR
You can use the READ RECORD directive, which will return the decompressed binary data of the compressed file in the archive.

If the file/record is a directory, the EXTRACT FILE directive will result in an Error #3: Input/Output error on file. The READ RECORD directive will return an empty string.

To use EXTRACT FILE, you must know the name of the file in the ZIP archive you want to extract.

EXTRACT FILE "new_filename" FROM (chan, KEY="filename")

If the path and filename of the file to extract are the same as what you want to put on your system, then you can leave out the KEY= option.

EXTRACT FILE "filename" FROM (chan)

PxPlus supports the following uses of READ RECORD for ZIP files:

Sequential - Where the files/directories entries in the ZIP archive are read sequentially in the order that they were added.

     READ RECORD (chan) data$

By Key - Where the key is the filename of the file within the ZIP archive.

     READ RECORD (chan, KEY="filename") data$

By Record Number - Where the record number assigned to the files/directory entries is based on the order that they were added into the ZIP archive. Record numbers start at one.

     READ RECORD (chan, RNO=recNum) data$

By Index Number - Where the index number assigned to the files/directory entries is based on the order that they were added into the ZIP archive. Index numbers start at zero.

     READ RECORD (chan, IND=indNum) data$

Appending to a ZIP File

You can append a file to the end of the ZIP archive in two ways:

Use the INSERT FILE directive, which will compress a file on your system and append it to the end of the ZIP archive.

Use the WRITE RECORD directive, which will compress binary data and append it to the end of the ZIP archive.

If the file/record is a directory, the INSERT FILE directive will result in an Error #3: Input/Output error on file.

To use INSERT FILE, you must know the name of the file you want to put in the ZIP archive.

INSERT FILE "filename" TO (chan, KEY="new_filename")

If the path and filename of the file to zip are the same as what you want to put in the ZIP archive, then you can leave out the KEY= option.

INSERT FILE "filename" TO (chan)

PxPlus supports appending both files and directories:

To append a file, use the WRITE RECORD directive, where the key is the name of the file to append to the ZIP archive, and contents contains the binary data of the file to add to the ZIP archive.

     WRITE RECORD (chan, KEY="filename") contents$

To append a directory to the end of the ZIP archive, issue a WRITE RECORD directive, where the key is the name of the directory to append to the ZIP archive, and contents is an empty string. Directory names must end in a '/' (forward slash) to be recognized as directory names.

     WRITE RECORD (chan, KEY="dir/") ""

Removing from a ZIP File

To remove a file/directory entry from a ZIP archive, you can use the REMOVE directive. PxPlus supports the following uses of REMOVE for ZIP files:

Sequential - Where the files/directories entries in the ZIP archive are removed sequentially in the order that they were added.

     REMOVE(chan)

By Key - Where the key is the name of the file/directory entry within the ZIP archive. If it is a directory name, it must end in a '/' (forward slash).

     REMOVE (chan, KEY="filename")

By Index Number - Where the index number assigned to the files/directory entries is based on the order that they were added into the ZIP archive. Index numbers start at zero.

     REMOVE (chan, IND=indNum)